An effective method of recycling is to compost the food wastes. However, this may be difficult, since food wastes tend to be more than 80% water. This hinders proper composting unless the moisture level is reduced. Furthermore, food wastes usually have a salt (NaCl) content of around 4%. This is also a significant barrier in the process of composting. Vermi-composting, using earthworms, is an environmentally friendly recycling method that does not require extra energy for composting.
How to Use Earthworms
It is quite simple to treat food wastes by earthworms. The steps are shown in Fig. 1. A little caution is needed in regulating the salt content and the acidity of food wastes for effective vermi-composting.
To keep the survival rate of earthworm above 60%, the salt content should be below 0.5% and the acidity (pH) of the food wastes should be above 6 ( Fig. 2). Salinity can easily be controlled by adding fresh water during the vermi-composting, which also improves fermentation.
However, food wastes which are too wet at the initial stage of composting may inhibit the earthworms from settling down. Saw dust or rice hull may be added to dry out excessively wet food wastes. To control the acidity to near neutrality, food wastes need to be fermented slightly before they are fed to the earthworms.
If the pH and moisture content are satisfactory, earthworms can be introduced directly at the initial stage. An increasing amount of food wastes can be mixed in as the earthworms adapt. Once the earthworms begin to feed on food wastes, the salinity and acidity are no longer a problem, as plenty of water is provided during the composting process.
The reduction of food wastes by vermi-composting proceeds so fast that the volume of the wastes can be reduced to a fifth of the original in one month ( Fig. 3). After composting, the earthworms can be harvested and used as a feedstuff, or as a raw material in the manufacture of health foods. In many Asian countries, earthworms are regarded as a good heath-enhancing agent. The remaining earthworm manure, together with the composted food wastes, can be used as an organic fertilizer or a bedding soil. Its chemical characteristics are shown in Table 1, shown together with those of swine manure compost.
The product from vermi-composting has various beneficial properties. It is a porous material with a pore size of 0.2 - 2.2 mm. It has excellent cation exchange capacity (CEC), water-holding capacity and air permeability, which make it very suitable for a soil conditioner. An experiment for its effectiveness as a bedding soil indicated that it doubles the growth of red pepper nursery plants, compared to those grown in an ordinary bedding soil ( Fig. 4).
Index of Images
Figure 1 Process of Vermi-Composting
Figure 2 Earthworm Survival Rate in Food Wastes with a Different PH
Figure 3 Efficiency of Food Waste Degradation by Vermi-Composting
Figure 4 Growth of Red Pepper Nursery Plants in Different Bedding Soils. Potting Boxes, from Left to Right: 100%, 75%, 60% 45%, 30%, 15% and 0% Food Waste Compost, Mixed with Ordinary Bedding Soil to Make 100%.
Table 1 Chemical Properties of Food Waste Compost and Swine Manure Compost
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